What is Foxing?

The term originated in 1848 and refers to scattered spots that are often reddish-brown (the color of a fox) on the surface of paper. According to Vlad Papov, Lowy's paper conservator, there are two major causes of foxing:

Fungal Activity:
Microorganisms found in the raw materials used to create paper can remain latent for years awaiting appropriate conditions for growth. Airborne spores can attach themselves to the paper, creating colonies of foxing.

Metal-induced degradation:
Metal impurities in paper resulting from particle abraded from pulpmaking equipment can cause a chemical reaction that results in foxing.

There are two different kinds of foxing: "Bulls eye" spots are small and round with two concentric rings. "Snowflake" spots, which got their name from their appearance under UV light, have scalloped edges and are much larger but are faint and usually cannot be seen with the naked eye.

Exposure to high levels of humidity for long periods of time and proximity to a poor quality, acidic support can also accelerate foxing. If the humidity of paper rises above 70% for an extended period (which is easy to imagine in a poorly ventilated cellar or attic) fungal growth will be stimulated and foxing will almost certainly occur. And if the artwork is also housed in an acidic cardboard mat, foxing can be even worse. "The good news," says Vlad, "is that foxing can usually be removed using a treatment of chloroxidation chemicals."